The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
The measurement of microvascular density (MVD) in tumors can provide valuable information to clinicians for evaluating and predicting the biology and clinical behavior of neoplasia. Additionally, MVD is an important variable to consider when evaluating experimental new treatments that target angiogenesis. For example, intratumoral MVD has been proposed as a prognostic factor in various types of cancer and as a marker for treatments that target blood vessels in cancer (Weidner, 1995a, b). Because angiogenesis is typically heterogeneous throughout tumors, it is often difficult to assess overall MVD by manually counting blood vessels in only a few selected portions of tumors (Costello et al, 1995). This difficulty in measuring MVD may be responsible for the various conflicting reports regarding the clinical significance of MVD in breast cancer (Medri et al, 2000), prostate cancer (Gettman et al, 1999; Abdulkadir et al, 2000) and thyroid cancer (Akslen and Livolsi, 2000).
Presently, MRI (magnetic resonance imaging) is a preferred functional assay for assessing blood vessel density within tumors (van Dijke et al., 1996; Brasch and Turetschek, 2000; Jensen and Chandra, 2000). The signal enhancement that is measured by MRI is a function of many variables that confound a simple determination of MVD, including the size of the contrast agent employed, the relative perfusion of the tumor, and the microvascular permeability within the tumor (Su, Muehler et al, 1998) For example, it is important to use a blood pool contrast agent that remains in the vasculature rather than a small contrast agent that quickly leaks into the interstitial space.
Other methods for assessing the functional status of tumor microvasculature include color-coded Doppler flow measurement (Peters-Engl C et al, 1998), positron emission tomography (Fanelli M et al, 1999), and uptake of albumin-Evan's blue dye (Graff et al, 2000). Recently, a number of histochemical methods have also been described for measuring intratumoral MVD. One method involves assessment of neovascular “hot spots” as highlighted with anti-factor VIII antibody (Weidner, 1995b). Other studies suggest that CD31 or CD34 might serve as markers for identifying blood vessels in tumors (Vermeulen et al, 1996; de la Taille et al, 2000). More recently, digital image analysis of breast cancer sections stained with monoclonal antibody to factor VIII has been proposed as a procedure for MVD assessment (Cruz et al, 2001).
There remains a need in the art for convenient, inexpensive, and accurate methods to measure microvascular density in tumors.